Merge Sort in Typescript

const merge = <T>(leftArray: T[], rightArray: T[]): T[] => {
    const mergedArray: T[] = [];
    let i: number = 0, j: number = 0;

    while (i < leftArray.length && j < rightArray.length) {
        if (leftArray[i] < rightArray[j])
            mergedArray.push(leftArray[i++]);
        else
            mergedArray.push(rightArray[j++]);
    }

    return [...mergedArray, ...leftArray.slice(i), ...rightArray.slice(j)];
};

const mergeSort = <T>(array: T[]): T[] => {
    if (array.length < 2)
        return array;

    const middle = ~~(array.length / 2);

    const leftArray = array.slice(0, middle);
    const rightArray = array.slice(middle);

    return merge(
        mergeSort(leftArray),
        mergeSort(rightArray)
    );
};

export default mergeSort;